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How does a nose down stall occur?
Imagine I am in a straight down dive, at terrific speed, and if I wanted upward sharp turn and got the stick back far enough, would I stall (or spin)?
Does normal laws apply when the aircraft nose is vertically down?

This is called a secondary stall: stall the plane and began a dive. During the dive, pull up till you get a stutter.

Does normal laws apply when the aircraft nose is vertically down?

Yes, always. Physics doesn't care much about the aircraft's attitude and cannot be switched into different modes.
While the nose points straight down, a stall is hard to achieve since no lift is needed - the weight is balanced by drag and inertia. However, when you pull abruptly and start to pitch up, the aircraft can stall while the overall attitude is still partially nose-down. If the pitch inertia is small, the rotation about the lateral axis will increase the angle of attack quickly while the flight path is still more or less straight down. At this attitude the stall angle of attack can be exceeded and the aircraft will stall. This is not unusual - pilots are routinely warned not to pull too hard after ending a spin. And yes, entering the next spin is entirely possible. This is especially likely when the sideslip angle has not been set to zero after ending the first spin. In most cases, this second, unintended, spin is in the opposite direction from the first spin because the pilot maintained his anti-spin rudder deflection for too long.
There have even been cases of supersonic spins.
A few details will help, though. A high pitch rate will delay the stall to an angle of attack up to 50% higher than the stall angle at zero pitch rate. Flying faster will increase the Reynolds number, so stall is slightly delayed when compared to the stall conditions at 1g. Both effects, however, will increase the wing root bending moment, and pulling out of a dive will run a real risk of breaking off the wings when you pull too hard.

Absolutely. Stalls occur when the critical angle of attack is exceeded, plain and simple. While it's easy to see this when the aircrafts nose is really high above the horizon it can actually occur at any attitude, even nose down or straight and level.
Angle of attack is determined from the oncoming relative wind and the reference line of the wing (the point from leading edge thru the trailing edge of the wing). So if you were to imagine the airplane headed completely nose down, the relative wind will essentially be coming from the ground. When you yank back on the control to change the airplanes path, momentum will keep the aircraft headed in the same direction (at least momentarily). At that point the wings may be level with the ground but the difference between the relative wind and the reference line will be enough to cause the aircraft to stall.


text:
Where is the wing sweep angle measured from?
If you look at a 747 planform wing you see something like this:

In several aerodynamics and aircraft design text books they use the wing sweep angle as an important parameter to measure the wing efficiency at transonic velocities, but they don't specify from where they measure that angle. Even I've seen wings with double leading edge angles.

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text:
What changes do narrow-body airliners undergo to serve (relatively) long routes?
I will try to pose a well-structured question here on the longest routes ever or currently served by small, narrow-body airliners - specifically, the Boeing 737 and the Airbus A319 and A320.
Set aside special versions in the likes of the Boeing 737-700BBJ, what makes a small, narrow-body airliner serve routes that are longer than those on which it is usually deployed?
Which is to say, what is added or changed, on the design side of things, to the structure or operability of planes that are not specifically designed for long distances, to make them capable of flying longer distances? I guess the answer is ETOPS, but I am not sure of what this implies from the operational standpoint.
For my moderate understanding it is quite impressive that narrow-body birds can fly from, say, Tokyo Narita to Mumbai - a distance of approximately 6,800 km or 4,220 mi (All Nippon Airways Boeing 737-700ER, flight NH829). Another example is Sunwing Airlines flight WG481 from Vancouver to Punta Cana (a Boeing 737-800 which flew for 5,930 km or 3,690 mi).
A list of such unusual performances can be seen here.

Because they don't have enough customer, or the airlines wish to provide more frequent services with smaller plane.

I don't understand what you mean - your answer seems truncated.

I'm a little unclear on what you're asking. Are you asking what Boeing & Airbus do to the planes at the factory to allow the 737/A32x to fly longer distances, or are you asking what an airline might equip a couple of their planes with to allow them to do duty on longer distance flights.

@FreeMan Basically, I am asking both.

Related: What is the main difference between an ETOPS certified and non-ETOPS certified plane?

Another rather extreme example of such a route operated recently was Houston to Stavanger, Norway, a distance of 4,844 miles. In this case, it was an all-business-class flight targeted at people in the oil industry (since oil is a huge industry in Houston and in Norway.)

The 737 ER (Extended Range) differs from the rest of its family by having an extra fuel tank extending its effective range.
Legally speaking (for US registered aircraft) you don't need to carry life preservers for each passenger, if you are only flying over land routes. So if a plane is being used for say a JFK $\rightarrow$ Nashville route, they would not be required to carry life preservers; but if they decided to use the plane on an over water route, they would have to outfit it as such.
Inter-Country travel may also effect the outfitting of a plane, as various countries have different equipment requirements (although most are the same now). Long haul routes may very well translate to non domestic routes, which means the plane may need to be outfitted with extra equipment that is capable of working on foreign systems.
There may be some paperwork involved around certifications as well. For example the FCC does not require domestically operated aircraft (commercial and GA) to have radio station licenses; however, it's often required by many foreign entities. A domestic only plane may need to obtain one of these licenses before heading to is destination.
On a bit of a side note the pilot must also be familiar with the destinations' regulations and methods of operation. For example here is a nice briefing from the FAA on flying into China.

Why long routes by narrow bodies?
Airlines use narrow bodies for medium-long range routes mainly for 3 reasons.

Demand
Market strategy
Fleet structure

Demand
Some airlines choose to service medium-long range route with narrow bodies simply because they don't have enough customers for bigger planes---like the 2 flights you have mentioned, both of them are cancelled because of insufficient demand.

Market strategy
On the other hand, some airlines are likely to provide more frequent services even with smaller planes. Business passengers are the main sources of income on those flights, they will pay extra for better a time that better suits them. That is common in flights between main cities between the east coast and west coast of the US. American Airlines uses the 3-class A321 to service 10+ daily flights between JFK and LAX (2173 nmi).
In addition, some airlines provide business-class exclusive services on the selected routes. Due to its relatively small demand, the airline will choose narrow bodies even for medium long route. BA Clubworld between London city and JFK is such an example, they service the 3000 nmi route by A318 with 32 full flat bed seats.

Fleet structure
Some airlines only operate narrow bodies, regardless of whether they are low cost carriers. So they service medium-long route only by narrow bodies, like Alaska 870 (Anchorage-Honolulu, 2418 nmi).

How long are routes by narrow bodies?
Both A320 and B737 series have "standard" 3000+ nmi maximum range when fully loaded, which can cover most of the "long" route. More accurately their MOTW starts reducing when range is over 2000 nmi. (Except B737-700ER)
It is hard to describe the payload/range in details. I would suggest you to have a look of it. (P.3-2-1 on A318, A319, A320, A321 & P.85-98 on B737 series)
ETOPS stands for Extended-range Twin-engine Operational Performance Standards, a rule which permits twin engine aircraft to fly routes which, at some point, are more than 60 minutes flying time away from the nearest airport suitable for emergency landing.
ETOPS is not a must when flying "long" routes, but it is necessary when flying over oceans or close to the Pole. Due to the limitation of the range, only a few routes require ETOPS, including a few transatlantic route (UK/Iceland - US East Coast), US West coast to Hawaii, as well as East Asia to Micronesia/Melanesia.

You mentioned 4 reasons?

@DanPichelman, and that's how you keep a StackExchanger in suspense... :)

On a more serious note, this addresses why an airline might choose to serve a longer route with a narrow-body, but not what they need to do to the plane to allow that to happen.

@DanPichelman Pichelman used to be 4, 1 paragraph for each.

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What is the angle of attack of horizontal stabilizer?
It 'appears' that in most flights the horizontal stabilizer is set for positive angle of attack.
So does this produce an 'up force' (lifting force) on tail thus making the aircraft nose-heavy?
Or does the horizontal stablizer presents itself to the relative air at a different angle of attack than the wing does (which creates down force on tail)?

it "appears" from where? also, what is not clear from your previous question?

Appears in the sense when I see that there is a positive angle of incidence. I thought means it is set for positive aoa.  Earlier question assumed that horizontal stab is fixed at 0 angle of attack and by using trimming its angle of attack is varied.

The AoA is between the airflow and the chord. But the airflow rear of the wing is not horizontal when the aircraft moves straight and level. Maybe the pitch is positive.

You are right, the horizontal tail of a conventional airplane appears to have a higher incidence, but the actual angle of attack is smaller than that of the wing.
The wing, flying ahead of the tail, produces downwash, so the flow at the tail location has a distinct downward component. The downwash angle can be calculated from the lift coefficient and the geometry of the aircraft: To simplify things, let's assume the wing is just acting on the air with the density $\rho$ flowing with the speed $v$ through a circle with a diameter equal to the span $b$ of the wing. If we just look at this stream tube, the mass flow is $$\frac{dm}{dt} = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v$$
Lift $L$ is then the impulse change which is caused by the wing and equal to weight. With the downward air speed $v_z$ imparted by the wing, lift is: $$L = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v\cdot v_z = S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho$$
$S$ is the wing area and $c_L$ the overall lift coefficient. If we now solve for the vertical air speed, we get $$v_z = \frac{S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho}{\frac{b^2}{4}\cdot\pi\cdot\rho\cdot v} = \frac{2\cdot c_L\cdot v}{\pi\cdot AR}$$
with $AR = \frac{b^2}{S}$ the aspect ratio of the wing. Now we can divide the vertical speed by the air speed to calculate the angle by which the air has been deflected by the wing. Let's call it $\alpha_w$: $$\alpha_w = arctan\left(\frac{v_z}{v}\right) = arctan \left(\frac{2\cdot c_L}{\pi\cdot AR}\right)$$
A typical airliner cruise lift coefficient is 0.4, and a typical aspect ratio is around 8: This results in a downwash angle of nearly 2° if the lift distribution over span is elliptical. In reality, it is more triangular-shaped, so the downwash angle is larger near the center of the aircraft. Note that the engine nacelles of the DC-9 and the MD-80 range are tilted 3° up to align them with the local flow.
The resulting angle of attack is lower by those 3°, and if the angle of attack difference between wing and tail is less than that, the tail surface will appear angled upward. To achieve static stability, the tail will have to fly at a slightly lower angle of attack than the wing.

so If I understand it correctly, air meets the tail at lower angle of attack when the horizontal stabilizer is placed at a positive angle of incidence? (thus producing less lift on tail surface)

@user2927392 The angle of attack is just the difference between flow direction and wing/stabilizer incidence. Increasing the incidence increases the angle of attack. The point is that behind the wing the local flow direction is different than ahead of it. This makes it appear as if the angle of attack at the stabilizer is higher when in fact it is lower.

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Why did the ATI B763 on May 26th 2022 return to LAX instead of landing at Naval Base Ventura County?
Looking at

 it seems they were right there, they had an emergency, surely even a civilian airplane can land at a naval base in an emergency. I know 767-300ERs used to fly from LGA which only have 7000 ft runways and NTD has a 11000 ft one. So, why not?

In general, a commercial airliner declaring an emergency can request to land at a military airport. However, this aircraft was at over 19,000 ft when they declared an emergency:

(flightaware.com ATN1917 on 26 May 2022)
Descending from this altitude takes quite some time. You can see on the altitude profile that they descended continuously shortly after leveling off. The descent rate is only shallower when reaching 10,000 ft (to slow down to 250 kt) and then when slowing further for the approach.
Landing at the nearby Naval Base would have taken the same amount of time. They would have had to descend in a holding pattern. Therefore, it makes sense to fly back to your departure airport, where maintenance facilities are available to get the aircraft repaired quickly:

The aircraft remained on the ground in Los Angeles for about 24 hours before returning to service.

(Aviation Herald)

Great answer. People often forget to think in three dimensions

It's not just maintenance facilities, landing at a commercial airport makes it much easier to get all the affected passengers and their luggage to their intended destinations.

@DanIsFiddlingByFirelight Prime Air does not fly any passengers, but people surely want their Amazon packages to be on time xD

You're saying that landing at NAS Ventura County would have effectively required falling out of the sky, and that's generally frowned upon by all involved, especially the pilots in question?

Also, LAX has a compatible ILS system, an approach they're familiar with and have charts for, etc. That is likely not the case at a naval air base.

@GavinS.Yancey There would be no difference at all in ILS procedures at the NAS, and any pilot flying into LAX would have the approach plates for KNTD as well.  If they were flying paper charts, all 8 approaches would be in the same book as all of LAX's, and if they are flying electronic charts, then they'd have them all as well.  There'd be no procedural difference between the two.

And if you're not familiar, you can do the math...  If you have to lose 19,000 feet, and will do it at an aggressive 1,000 FPM, then you need 19 minutes to get down.  And at about 5 miles per minute of speed, you'll cover close to 100 miles in that 19 minutes.  If you want to cut that to 30 miles, you either need to slow way down, or descend at an ear-abusing 3,000 FPM.  They were about 40 nautical miles out.  It's not unusual for an airliner to begin descending over 200 miles from the destination airport.

Thanks, I simply didn't realize they already were this high up.


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Has it happened before the EASA and the FAA disagreed on the airworthiness of a plane?
With the Continued Airworthiness Notification and with the updated statement https://pbs.twimg.com/media/D1fZ4GTW0Ac4Qsr.jpg in contrast with EASA   2019-0051-E it is crystal clear the EASA and the FAA disagrees on the airworthiness of the 737 MAX at this time. Had this happened before?

It seems FAA and EASA did disagree since 2016 about 737max certification, and not just after the crashes. EASA certification was conditioned by training and more information to the pilots, which hasn’t been done.
Please refer to the following website:
https://www.cnbc.com/2019/03/29/reuters-america-insight-regulators-knew-before-crashes-that-737-max-trim-control-was-confusing-in-some-conditions--document.html
You read the following:

The European Aviation and Space Agency (EASA) certified the plane as safe in part because it said additional procedures and training would “clearly explain” to pilots the “unusual” situations in which they would need to manipulate a rarely used manual wheel to control, or “trim,” the plane’s angle.

You may also read about EASA:

The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said:
It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s centre console rather than an electric thumb switch on the control yoke.

So when agencies give their approval it doesn’t mean the approval conditions are the same, it was not the case since the origine  for the 737max, and not just after the crashes.

This is the type of answer we're looking for, @user40476! It's got details, quotes and a source for the quotes! Thank you!!

Yes, it happens with most aircraft when they are first certified.  The dates of certification by the FAA and EASA would rarely be identical, so there is some period where a new airplane is considered airworthy by one, but not the other.  As you are asking about the 737, the EASA TCDS shows that it was first certified by the FAA on Dec 15, 1967, and has an EASA validity date of Jan 23, 1968.

Nobody is denying EASA certification. The quote is saying that additional training was required for pilots by EASA. FAA did not request that specific training.

You misunderstood my answer.  They disagree about the airworthiness.  One had certified it as airworthy, the other had not (yet).

Yes with respect to the CONCORD supersonic which had different limitations due to the produced supersonic subsonic transitional external sound.
As you say recently with respect to the 737 max, since it has been forbidden flight in Europe irrespective of FAA decision which came well later on.

The question is whether or not the two agencies had a disagreement before the 737 MAX.

@TannerSwett he did mention the Concorde which was well before the MAX, though it's not clear (from the answer) whether or not the Concorde disagreement was about airworthiness (as the question asks) or about where it was allowed to fly due to the sonic boom. Additionally, he'd have done better to have combined his newer answer with the existing one.


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What forward airspeed produces maximum rate-of-climb in helicopters?
Lift in a helicopter increases with airspeed (from zero IAS up to some Vmax).  But in contrast to fixed-wing aircraft a helicopter can generate lift at zero airspeed.
Is there a formula for the airspeed at which a helicopter achieves it maximum rate of climb?

"a helicopter can generate lift at zero airspeed" the speed you mention is not the airspeed, but the forward speed.  To be at zero airspeed you would need to stop the forward motion, but also to stop to rotor, the rotor is a rotating wing creating its own airspeed and lift. Actually this forward motion increases lift on the advancing blade but decreases it on the retreating blade, creating an unbalanced rotor load.

There are a couple of things at play here:
First, the increase in overall lift of a helicopter as it correlates to an increase in forward airspeed actually has a lot to do with the establishment of Effective Translational Lift (ETL) or the airspeed at which the entire rotor system realizes the benefit of the horizontal air flow. This happens when the helicopter's rotor disc moves completely out of its own downwash and into undisturbed air.
Second, beyond the ETL improvement, forward airspeed in a helicopter only produces an increase in asymmetrical lift, rather than the the nice, tidy symmetrical lift dispersal of fixed wing aircraft. This is because of a principle known as (surprise, surprise) Dissymmetry of Lift. The forward airspeed is added to the rotational speed of the advancing rotor blade on one side of the aircraft and subtracted from the retreating rotor speed on the opposite side of the aircraft. While this is counteracted to some extent by mechanical adjustments (flapping, feathering, leading-lagging) to equalize the inherent rolling tendency, this means that the forward speed alone, as a catalyst for lift production, is not the be-all and end-all.
You are correct that a helicopter, under the right conditions and possessing a surplus of available power can generate lift at zero airspeed. This is why a helicopter, under these conditions, effectively has a Vx of zero, since its best angle-of-climb over distance would be a straight vertical climb.
For Vy, the best rate-of-climb over time performance, it is important to plan for torque settings at level flight. Climb performance charts show the change in torque, above or below torque, required for level flight under the same gross weight and atmospheric conditions to obtain a given rate of climb or descent.
Here is a sample calculation taken from the FAA Helicopter Flying Handbook:

Determine  torque  setting  for  cruise  or  level  flight  using  Figure 7-7.
Pressure Altitude = 8,000 feet,  Outside Air Temperature = +15 °C,  Indicated Airspeed = 80 knots,  Maximum Gross Weight = 5,000 lb.

With this chart, first confirm that it is for a pressure altitude of 8,000 feet with an OAT of 15°. Begin on the left side at 80 knots indicated airspeed (point A) and move right to maximum gross weight of 5,000 lb (point B). From that point, proceed down to the torque reading for level flight, which is 74 percent torque (point C). This torque setting is used in the next problem to add or subtract cruise/descent torque percentage from cruise flight.
Determine climb/descent torque percentage using Figure 7-8.
Rate of Climb or Descent = 500fpm,  Maximum Gross Weight = 5,000lb.

With this chart, first locate a 500-fpm rate of climb or descent (point  A), and then move to the right to a maximum gross weight of 5,000 lb (point B). From that point, proceed down to the torque percentage, which is 15 percent torque (point C). For climb or descent, 15 percent torque should be added/subtracted from the 74 percent torque needed for level flight. For example, if the numbers were to be used for a climb torque, the pilot would adjust torque settings to 89 percent for optimal climb performance.

As you can see on chart 7.7, the green line represents the Vy speed and is relatively low, because it represents the speed at which the lowest percentage of maximum torque is required to sustain level flight in the given conditions, and thus, the speed at which there is the maximum amount of surplus torque available to climb, all while remaining in ETL flight.

Above certain weight and altitude, $V_x$ is not zero, because the helicopter is no longer able to sustain hover out of ground effect. In the first diagram the 5,000 lb gross weight line is way above the max torque available indicating hover is not possible at the weight and altitude.

The above explanation is really good. Another way to simplify the answer is to consider the two main areas of drag associated with helicopters and the power required to overcome this drag. In the hover Induced Drag is a maximum and this reduces with increased speed whilst Parasite Drag is a minimum in the hover and increases with an increase in speed. Where these two graphs cross, would represent the maximum power margin and the speed for the maximum rate of climb (fig.7.7). For most helicopters this normally occurs between 60-70kts.
To answer your question, yes there could be a formula to calculate  the best rate of climb for a specific helicopter, but as there are many variables associated with this calculation such as density altitude and   AUM etc a performance graph is normally used.

I find that the easiest way to visualize the answer is with a "power available" chart, which shows both the power available and the power required.

Above is a chart from an article by Frank Lombardi, "Understanding Helicopter Power Requirements: The Power Struggle", Rotor & Wing International (Oct 10, 2017)
The best rate of climb is where the total power required curve is at the lowest. As the article explains:
"Total power [required] continues to decrease with increasing airspeed, until you reach the “bucket” speed. This is the point of greatest difference between power required and power available, which can be translated into maximum rate of climb." (word in brackets added)
This kind of chart takes into account things like translational lift, which reduces the power required as forward speed increases.
Coming up with a universal equation to compute the speed at which total power required is at the minimum could be a nightmare. This is because - as the chart shows - a helicopter has several components which consume power (the FAA refers to them all as drag). These are: (1) profile drag; (2) induced drag; (3) parasitic drag; and (4) miscellaneous drag. Each component has a different equation, some of which are very complex.
But even if you go to all the work to create an equation which includes all these components, you should be aware that, with helicopters, even the best equations are notoriously inaccurate. As one author noted: "Hover performance cannot, even today, be predicted to within ±5 percent" [Franklin D. Harris, "Introduction to Autogyros, Helicopters, and Other V/STOL Aircraft", Vol. II Helicopters, p. xi]
So, if you are going to fly a helicopter, you should use the published tables described elsewhere. These contain adjustments for altitude, which are critical for a helicopter.
If you just want to solve an equation for fun, you could use curve fitting to create an equation that closely matches the bucket in the power required curve and then solve for the minimum value.


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Can the V-22 autorotate?
Can tilt-rotors like the V-22 execute an autorotation landing?
If so, are the conditions under which that would be possible (and survivable) different from a helicopter?

Closely related: If an Osprey found itself unable to rotate its engines to vertical, what would be the emergency procedure for landing?

This seems to be a hot topic - in principle, the V-22 should be able to fly and land in autorotation, but tests so far did not demonstrate this. The manufacturer's position is that autorotation was never part of the specification.
What it comes down to is the inertia of the rotating parts relative to the aircraft's mass. The requirement to fold the rotors put a limit on their diameter and consequently their inertia while increasing their disc loading. The inertia is too low to reduce the rate of descent enough to enable a safe and soft landing. Quote from Wikipedia:

While technically capable of autorotation if both engines fail in
  helicopter mode, a safe landing is difficult;[73] in 2005, a director
  of the Pentagon's testing office stated that in a loss of power while
  hovering below 1,600 feet (490 m), emergency landings "...are not
  likely to be survivable."

This is specific to the V-22 - other tiltrotors might well be able to land in autorotation if their rotor inertia and speed is high enough.
For all practical purposes, the V-22 can glide down in autorotation, but will not be able to perform a soft landing at the end of this glide.

So it is able to generate some lift by autorotating its propellers in the vertical position?  I imagine there would be one envelope for gliding in forward-flight configuration (i.e., fixed-wing-style power-off landing), and a different envelope for autorotation.  The "inertia" you refer to is literally the mass of the propeller blades (and hub)?

@feetwet: The recommended power-out mode is to glide like an aircraft with vertical proprotor position, so they work as impellers and drive the hydraulic pumps and electrical generators. Classical autorotation is possible, but the sink rate is too high for a soft landing. Inertia is the integral of the mass over the distance from the center, so both mass and proprotor diameter are involved.

I guess that's the "real" answer for the V-22.  But it leaves me wondering whether, given that the props are linked to the hydraulics and generators, one couldn't backfeed enough power from batteries and pressurized reservoirs at the last moment to power a landing flare?

@feetwet: Let's consider the energy change needed for that. The sink rate of the V-22 in autorotation is 18m/s, the mass is 20 tons. For landing you need to get rid of a kinetic energy of 0.9 kWh. Say you decelerate the V-22 over 2 sec by one additional g. This would require an energy of 1,600 kW on top - much more than any generator or battery can deliver. You need an operational aircraft engine, and that is without any losses or reserves, and without adding what you need for lift. Either at least one of the engines is running, or the V-22 hits the ground hard.

There is nothing that prevents tilt rotors from performing an autorotational landing, in theory. AugustaWestland AW 609 has already demonstrated this. The Bell XV-3 also did this.
However, V22 has not demonstrated autorotation in any practical sense. The descent rate is too high for safe landing. The failure of V 22 to autorotate is due to the high wing loading (which is ~50% high compared to the AW609) and the low inertia of the blades.
The manufacturer/operator has instead claimed two things- the requirement (of both engines failing together) is remote and that it can glide in any case. At the end of the glide (which is pretty steep compared with 'normal' aircraft), the structure and seats are expected to absorb the impact.

If hovering, it will need quite some height to get into a gliding state. Since there seems to be no autorotate procedure, and this capacity seems to be doubtful, then we should best ignore that option. This means that it will basically fall like a brick and crash if it does not have enough height to transition into "aircraft gliding state" the this only supports the claim mentioned earlier (made by "a director of the Pentagon's testing office") that a failure under a specific altitude in hover mode would not be surviveable.

I read there was nothing in the specs to require autorotation like a traditional helicopter.  I also read that the glide path to accomplish an auto would be too steep to go to a run on landing, which is recommended for single engine out procedures.  The only time there is not sufficient altitude for an auto is when you are at a hover below 1800 feet, which is rediculously high to hover and I am not sure what mission would require that task. Even in a normal helicopter flying low over the trees does not allow much time to decelerate, speed up the rotor in time, and cushion landing with rotor inertia momentum.  Cushion is what the traditionalists are looking for.  Only the most superior pilot will stop all forward movement and not hit any obstacles when terminating at the ground without power.  The Osprey meets its specs.  And, all the other points are mute without the best pilot that exists at the controls, which is only the Senior Instructor Test Pilots or Acrobatic Pilots, which are not a part of the training.  Just stick with run on landings and avoid hard wood trees at the bottom. There is no need to fuss over the Osprey ability to fully autorotate when landing.

You may add references and links to support your answer and to provide further reading.


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If I ferry an aircraft to the United States (from say the UK) is it a commercial or private flight?
If I am paid to ferry an aircraft from the UK to the US and then leave the aircraft in the US, is it a private or commercial flight?
I am not carrying passengers or cargo, but perhaps the aircraft itself becomes cargo if it is left in the US.
I guess my question follows on somewhat from this below:
What is the difference between a private and a commercial flight according to the US Customs and Border Protection?

Private or commercial according to whom? CAA, HMRC, FAA, CBP, ...?

Are you being paid for it?

@RonBeyer first four words of the question ;)

If you are being paid, in the EU or US at least (I suspect all jurisdictions will be the same), then it's commercial.  The only payment you may take as a private pilot is to reimburse direct operational expenses you have paid and providing that you pay at least a pro-rata share of those expenses (i.e. receive back only the expenses minus pro-rata deduction).

@Simon I don't believe he's asking in terms of FAR's but US Customs rules.

This question was answered in an earlier (2013) message.
Generally, if you are ferrying an airplane and are compensated as a commercial pilot, are not carrying passengers or cargo for hire, you are operating under Part 91 of the US federal aviation regulations.  That you are a paid ferry pilot is not relevant.
See 19 CFR 122.1(d) A "commercial aircraft" is any aircraft transporting passengers or cargo for money or other consideration.
As you are not transporting passengers or cargo (both of which would be covered under the commercial operator rules) or you have a passenger as a friend or the aircraft owner who does not pay for passage, you are ferrying an aircraft which is covered as a private flight.
Make absolutely certain you understand how the US eAPIS system applies to you as a foreign national bringing the aircraft into the US, and you have appropriate documentation and the owner is prepared to jump through whatever hoops Customs needs to get the aircraft ashore.  The US Customs Guide for Private Flyers is a useful reference.
Simon, I disagree with your understanding.  There are many operations which are not commercial, with paid pilots.  An example of this is a corporation owns an airplane which requires a pilot.  The corporation can hire a pilot to fly its airplane and carry its parts/executives/employees/friends.  While the pilot must carry a commercial certificate and carry at least a Class II medical certificate, the flight is not considered a commercial flight, nor is the the company considered a commercial operator since it does not hold out its aircraft for hire, unless its in the air carriage business.  If on the other hand that same aircraft owner decided to carry the company next door's freight and executives and charge them for it, that changes the story.

Thanks so much. This is what I was leaning towards. It's all a bit of a gray area as I'm organising, for my airline, the movement of an aircraft for sale. As we hold an AOC but are operating this as a private flight it all gets a bit muddy.


text:
Why do some airfields not have a climb gradient for LPV?
Can anyone advise why for some airfields there are minimum approach climb gradients for LNAV with none for LPV, while at other airfields there are minimum approach climb gradients for both LPV and LNAV?
This is an extract from the plate for Campbeltown - EGEC.

For other airfields, MPA gradients are also given for the LPV as well as LNAV such as Islay - EGPI, shown below.


text:
Why can't armrests be raised on window and aisle seats?
I noticed that armrests on all the flight's I've taken recently can't be lifted on aisle and window seats (the edges of a row).
Last time I flew, I got lucky: I was alone on my row and as such I was able to lay down to sleep. However, it was hard to make myself comfortable as that armrest was pressing on my spine when I tried laying down with my back to the window.
Also, it would be much easier to get out of my aisle seat if I could lift the armrest. I'm a pretty tall guy, so I always feel like a contortionist trying to get out of my seat.
What's the problem with letting people raise the armrest on window and aisle seats?
I'm guessing it's some sort of safety issue, because the mechanism seems to be the exact same one as the other seats, just with an extra locking mechanism added.

Apparently, it can be done, atleast in some aircraft; even in those cases, the armrests are locked, unless one knows the location of the release button.
As for why, it seems that there is a possibility that the upright armrests can be an obstacle (for people in the next seat row) and FAA expects the cabin crew to ensure that the armrests are in forward condition prior to takeoff/landing. According to FAA Volume 3, Chapter 33, Section 3 Instrument and Equipment Requirements,

Inspection of the Hardman Model 9500 and other passenger seats installed on several aircraft, disclosed that the armrest in the upright or stowed position can protrude approximately 45 degrees aft the seat back. In the event of an emergency evacuation, protruding armrests could present an obstacle between seat passageways, obstructing emergency exit access. Air Carriers should emphasize to F/As that prior to takeoff and landing they verify that the armrests are in the normal forward/down position in order to ensure that they do not obstruct the passageway between the row of seats leading from the aisle to the emergency exit.

As this is a problem in aisle seats (armrests in middle seats cannot go back usually), they have to be fixed forward or atleast locked in position. This is the reason for them to be locked in case of aisle seats. As for window seats, the sets are usually made in a row and you don't really know if the seat will end up in window or aisle i.e. whether the row will get fixed on left or right (or middle, in widebodies). Net result is that both the ends of the row are fixed just to be sure. In other words, the windows armrest is a collateral damage.

"collateral damage" yields you a +1! :)

Why can't they just add a detent / stop so that the upright stowed position does not go beyond the vertical & protrude into the back row?That should obviate the FAA concerns about evac safety.

This might be the correct answer for aisle seats but the window armrest is actually different rather than symmetrical: for the aisle armrest there's a hidden release button you can use but for the window one no such button is available.

On aisle seats it can be done, most of the time. In 20+ years of flying around Asia and Europe, I have been unable to lift the aisle armrest only once, I think, on an LCC. The rest of the time, all I had to do was look for the button or switch under the armrest, towards the back. Lately (2023) I have noticed on newer planes that the button is not inside a hole in the armrest, but a button/switch flush with the hinge. YMMV.
I usually raise the armrest halfway through, at about a 90° angle, as soon as I sit down, because harried travellers with a crapload of carry-on luggage and no spatial awareness tend to bump into me (and many other people). Instead, they bump into the armrest, and go ouch, instead of me. Once in a while, FAs ask me to lower it, and I politely decline – after boarding is complete, ma'am...
I've had travellers across the aisle ask me "How do you do that?" – they seemed happy to learn that little trick... It is also helpful when standing up.
I never fly on window seats, if I can help it, so I never tried it there.


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How do you choose engine placement for under wings engines?
I'd like to know how you choose the location of the engines under the wings, in the case of a 4-engines aircraft with low wings (and therefore with engines under the wings).
Concerning the longitudinal location, what are the constraints? Nacelles are usually in front of the wing, but why? I know there is a security constraint, especially with high bypass ratio engines, but is that all?
Concerning the lateral position, you want to reduce the bending moment of the wings, and therefore have your engines close to the wing tips during flight. But one could also say you want the engines close to the CG to reduce bending moments on the ground... Which constraint is dominant? And why can't we have to engines close to each other? (far enough to avoid flow interactions)

for the forward position, see here (and the other linked question): http://aviation.stackexchange.com/questions/16499/1467

Possible duplicate of Why do we use pylons to mount engine on jet airliners?

@fooot, I disagree with the duplicate - that question does a nice job of addressing how far below the wing to hang the engine and why, but not how far away from the wing root. It does cover some of the how far in front of the leading edge should it go, but I'd imagine we'll get even more detail about that on this question.

After having read aeroalias' picture collection, I feel an urge to chime in.
Longitudinal position
The main reason to place them ahead of the wing is flutter suppression. Flutter is an oscillation caused by the interaction of elastic and aerodynamic forces. In case of the wing, it is an up-down bending motion. Since air takes its time to flow over the wing, at a certain airspeed the air pressure change on the wing is so much out of phase with the motion that it amplifies the elastic motion of the wing. By placing the center of gravity of the aircraft part ahead of its elastic axis, flutter can be suppressed. This is true of flaps (where a mass balance is added ahead of the hinge line) as of full wings (where engines take the part of the mass balance).
Imagine the wing bending up, and now add the inertial forces of an engine connected to this wing and also moving up. If it is placed ahead of the elastic axis, it will induce a torsion moment into the wing, such that the local angle of attack is reduced, which in turn will reduce lift and the forces which cause the wing to bend upwards. The same happens in opposite direction when the wing bends downwards. Since the biggest thickness of the wing is in its forward section (which shifts the elastic axis forward) and the heavy flap mechanism is in its rear section (which shifts the local center of gravity back), a wing without an engine mounted forward of it needs a much heavier structure or less heavy, but otherwise unproductive, balance weights.
Placing the engine ahead of the wing brings some more benefits:

Airflow at the intake is less influenced by the pressure field of the wing, so the variation in local flow direction is smaller, resulting in a better-performing intake.
An uncontained turbine failure is less likely to damage the wing.
The engine can be mounted higher relative to the wing, such that the landing gear can be shortened.

Why engines are not placed on top of the wing is discussed in this answer.
Lateral position
In two- and three-engined jets you put them at the wing station where the inner wing ends. The main reasons are:

There is a major rib anyway to support the wing's skin, so the structure for attaching an engine is easier to add.
There is a gap between inner and outer flaps (at least in Boeing designs), so the engine blast will not hit the flaps.
They are still relatively close to the center of the airplane to not require an excessively large vertical tail to cancel the yawing moment in single-engine flight.

Boeing 737 bottom view (picture by Adrian Pingstone). The inner wing section has an unswept trailing edge while the outer wing has less taper and a swept trailing edge. The engines are exactly where both meet.
Aircraft like the DC-8 had their inner engines at the wing rib which supported the inner flap tracks of the outer Fowler flap, because they had no gap between inner and outer flaps. On the DC-10, Douglas placed the wing engines at the break between inner and outer wing, however.
In four-engined jets the inner engines are placed like those on two-engined jets, while the outer engines are placed at the end (or slightly outside) of the outer Fowler flaps, about midway between the inner engine and the wing tip. Note that again a rib is needed where the aileron cutout starts - this rib doubles as the engine mount. There the engines can contribute a lot to bending relief, and since a single engine contributes only 25% of the total thrust, the yawing moment of the outer engine in the engine-out case is roughly equal to that of a single engine of a two-engined jet.

Airbus A340 bottom view (picture by Adrian Pingstone).
Why it is better to separate the engines and spread them out over the wing instead of collecting them in a single nacelle is explained in this answer.
In some cases, the engine location is dictated by other requirements. On the Antonov An-70 the inner engines need to be far enough out to allow to drop paratroopers from the front door, for example.

Any design decision is an optimization problem which involve a number of diverse factors. There are multiple parameters to consider while determining the location of engines in the wings.
Longitudinal location

Clearance- In case of high bypass turbofans, farther the engine is out in the wing, greater is the clearance in ground (and require less landing gear length). In some cases where high bypass engines were retrofitted on aircraft, the engine inlet shapes had to be non-circular to get the required clearance.

CFM56 engine on Boeing 737, Image from asec.ir

Interference- The engine mounting (pylon and nacelle) interferes with the airflow over the wing, which affects the longitudinal location.
Safety- Any uncontained failure of the engine disks should not damage the primary structure of the wing, which influences the longitudinal location of the engine. Also, any engine (part) failure should not affect the wing leading edge devices. For this reason, the engines are mounted well in front of the wings.

Typical engine mounting, from adg.stanford.edu

The longitudinal location is also affected by the requirement of operating thrust reversers, which basically deploys a section of the nacelle aft and out.

Boeing 787 thrust reverser operation. Image from www.pbase.com

The location of the engine center of gravity forward of the wing produces a torsional moment, which has the effect of increasing wing stiffness.

Lateral Location:

Stability- Closer the engines are to the fuselage, lesser the yawing moment in case of an engine failure.
Control surfaces- Usually, control surfaces i.e. flaps are not present aft of the engine as the high temperature flow requires special materials. This leads to reduced Cl_max. The following figure clearly shows the absence of high lift surfaces aft of the engine.

"Undercarriage.b747.arp" by Arpingstone - Photographed by Adrian Pingstone in August 2002 and released to the public domain.. Licensed under Public Domain via Commons.

Drag- In this case, engines buried in the wing root is the best location. However, it is rarely used due to various reasons- difficult engine maintenance, wing redesign required if a new engine is to be used, elimination of inboard flap, etc. The location of the engine also affects the interference drag (with the fuselage).

Effect of large engine on interference drag, image from adg.stanford.edu

Wing loads- The location of the engine in the wing helps to relieve the wing bending moment in flight (as for reducing the bending moment in ground, compare the flight and ground loads).

The location of engine is determined after considering all these (and many other) factors.


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Why is being a commercial pilot stressful?
Being a commercial airline pilot regularly appears around the top of "most stressful jobs" lists.  I do not doubt that this is a stressful job, but as an outsider with no aviation experience whatsoever I do not understand why.  I am curious to hear a first-hand explanation.
I have always imagined flying long-haul to become very tedious and repetitive after a while.  The only significant source of stress I can see is time away from family/relationships (which admittedly I couldn't cope with, but it doesn't seem sufficient a reason to propel this to the front of most stressful professions).

@Pondlife opinion-based, yes. But the other question doesn't answer the "stress-question".

Voting to reopen, it's a good question, it can be answered without too much opinion involved, there are a lot of facts that are well known to be stressful. (And BTW, the other question is closed).

I also voted to reopen. The question can be answered with specific examples that clearly illustrate why it can be so stressful. The stress comes from many things, but generally speaking,much of it can be traced to three sources: physical abuse of the body (i.e. massive time zone changes, following an irregular work pattern), uncertainty (what will happen is often independent of your actions), decision making in the face of incomplete information. If the question is reopened, I'll answer with detailed examples.

"What's stressful about flying 6 miles up in the sky at 500mph, in a storm, with 600 people relying on you to stop a metal tube plummeting into the side of a mountain, using about 500 buttons/switches/levers/dials/pedals etc?"

I heard airport dispatcher's job is extremely stressful, not the pilot's. Not that pilot's job is stress-free of course.

@JonStory Don't forget that the metal tube is worth hundreds of millions of dollars

The stress comes from everything about the job that isn't actually flying the plane.

Dealing with crew scheduling is the #1 cause of stress.  If your phone rings with that special ringtone you assigned to them, you know nothing good is going to come of it.  These calls often end with reassignments, changed overnights, different crew members and sometimes extensions into days off.
Dealing with a stubborn dispatcher who, despite the mess of storms on your route, refuses to give you an extra 500# contingency fuel.
Dealing with pressure for on-time departures.  This usually comes from a gate agent because they generally are the ones who get the short end of the stick if we push late.  This can be exacerbated by agents who know about certain "tricks" to fool the system into thinking you pushed, which are often specifically disallowed by flight operations.
Winter operations.  Figuring out where de-ice happens, what special flow control might be in effect and managing holdover times can be a headache, particularly at unfamiliar fields.
Spring and summertime.  Never a moments rest during cruise but instead a constant look on the horizon and the radar and requesting deviations from every controller you talk to.  These seasons often have days with widespread thunderstorm activity.  These storms for the most part must be avoided and sometimes require constant coordination with controllers to deviate off-route to go around them.  This creates fatigue more than stress, but the two have a way of feeding back on each other.
Holding.  Do we really have the gas to be doing this?
Diverting.  Coordinating with dispatch, maintenance (if needed), operations at the field, ATC and passengers.
Timing out.  Hey folks, sorry we diverted but now we timed out, we're staying the night here.
Crew scheduling, again, to get hotel rooms and find out just how bad this day screwed our schedules for the next few days.
That once yearly visit to the AME where you are reminded just how bad your airport junk food diet is and where exactly "hypertension" starts.
Commuting.  It is fairly common that pilots do not live in their base and live far enough away that the commuting means jumpseating or non-rev flying to get to work and back home.  Depending on where you live you can often encounter oversold flights, competition for the jump seats and little backup options for same-day travel (e.g. not flying in the day before your trip).  Not making it work can have consequences depending on how hard you tried to make it work and how good your union contract and chief pilots are.

Of note, I never found actually flying the plane stressful including operations in low visibility and high winds.  Those are the things that kept the job interesting and I quite enjoyed them.  Having people in the back was also never stress inducing.  As long as I flew safely and kept myself alive, the passengers would end up that way also.  I was mindful of the passengers in selecting alternate cruise altitudes for ride conditions and requesting shortcuts from ATC to make up time but those are not stressful things to do.

To the passengers it's all about a smooth landing..

Once yearly visit? Are first class medicals now good for a year?

@Terry For a few years now. Probably my favorite reg change.

Wouldn't "The welfare (and lives) of 200+ passengers literally are in your hands" rank pretty high up on the list? I know I'm stressed just driving the van pool and that's only 5 people.

@Johnny Not really. Finding a good altitude and being on time isn't really stressful I don't derive stress from having souls on board mostly because if I keep myself alive, they stay that way too.

@terry Only until the pilot turns 40, then it's back to every 6 months.

@mins the passenger is a consumer. They pay for the service including pilot effort. It is not for the consumer to worry about how difficult it is beyond the price tag. A thank you is nice (i always have a word with the crew if I've had a positive experience) but ultimately it is like a tip - optional.

@Gusdor: So why do they clap when the pilot lands? Do they think it's not included in the price? Not an actual question indeed! I often hear and read about pilots being too much paid for doing nothing (everything automated today).

@mins what I was trying to say is - feedback from the passengers should not be an expectation. Applause in after a high wind landing is a good way of relieving the stress that everyone in the cabin feels.

It sounds like most of these points apply to any driver's job. Concentrating on the road all the time, figuring out an unfamiliar car wash/parking, winter operation, junk food... And why is scheduling such a headache? Does the pilot manage the entire crew, order hotel for them, etc?

I never thought about the Pilots as managers - is this true across the board? or are some commercial pilots just pilots (dealing with the plane, and getting it from the gate to runway to runway to gate and all the talking in between). If pilots tend to do crew scheduling, who selects them for the plane? who makes hiring and firing decisions? etc...?

@CodeJockey You should post a new question to get those answers

@casey OK if you stay alive your passenger probably also stay alive. But you may deal with medical emergencies.

My grandfather didn't fly commercially, but he was a general practitioner and a private pilot. He was really upset when his vision degraded to the point that he couldn't fly anymore. He was still able to perform physical exams for pilots and the hardest thing was to tell a pilot that he couldn't fly anymore.
As someone who has had to be a manager, I completely understand. You're the proverbial duck on still water and it feels like your duty not to let the people around you know just how much you're doing to keep things running.

Can some explain the "Spring and summertime" point?

@bobbyalex Thunderstorm season. Can't go over, can't outclimb so you need to go around. This involves requesting route deviations with ATC.

@casey Spring/summer meaning thunderstorms is very geographically dependent. There are very few thunderstorms in the UK, for example. I think it would be much clearer to phrase it as "thunderstorm season" in the answer.

@casey, Hi, how did you manage to be both a programmer, meteorologist, and an airline transport pilot (as noted in your profile)?

@Pacerier Find me in chat if you want an answer to that.

The amount, types, duration, and severity of pilot stressors vary widely. The individual airline, union involvement, scheduled versus non-scheduled, international or domestic, type of equipment, freight or passengers, everything has an effect. I look at pilot stress within the context of what I was doing the last 10 years of flying 747s on international routes for two carriers. For me, the stressors usually (but certainly not always) were of three types: physical abuse of the body, decision making in the face of incomplete information, and frustration over things I had little or no control of. The examples below are from the 1990s, but I'm reasonably certain like things and conditions still occur. There are still 747-200s flying, not many, but two of them are SAM 28000 and SAM 29000, the President's two 747s (heavily modified of course).
Physical Abuse of the Body
For me the biggest stressor was the massive time zone changes. The last five years I was based out of JFK, but I lived in Oregon. After I collected a little seniority, I typically had 12 days off in a row each month, but a day of that on each end was given over to commuting.
Thus a work period began with the hassle and uncertainty of jumpseating for a multiple leg, minimum 2500 mile journey and a 3-hour time zone change to JFK. The most typical next day was JFK to Tel Aviv, a 12 hour flight and another 7-hour time zone change. We left JFK in late evening, arrived at the hotel in Tel Aviv in early evening of the next day. I would wake up in Tel Aviv around 0200 local, and from that point on through the rest of the work period, my circadian rhythm was totally screwed up.
We did a lot of charters, and that introduced a great deal of irregularity into our schedules. It was not uncommon to have a charter come up that would take us off the line that we bid for and was awarded, and from that point on we usually did not get back to the awarded line. Thus we often would not know what we would be doing after we completed the current flight until we got the call in the hotel after the flight.
If you operate often into third word countries, you may occasionally get sick. It happened to me twice in 10 years, once in Jakarta at the Hilton, and once in the Ramada just off the airport in Delhi. The Jakarta Hilton had a 24/7 clinic in the basement, primarily for their employees but available to their guests, so it was no big deal to have a doctor come up to my room in the middle of the night and give me a shot to control the vomitting and diarrhea and stop the dehydration. The Ramada was a much smaller hotel, so they had to call out a doctor from home, again in the middle of the night. We had no reserve captains in Delhi. I operated a Hajj flight the next day with a hand towel arranged as a diaper.
Decision Making in the Face of Incomplete Information
This happened all the time. It was part of the job, took many forms, and meeting the challenges was part of the fun, but it was stressful. For example, we picked up a planeload of U.S. Army troops at Stewart Air National Guard Base in New York to take to a recently constructed runway in the Balkans. We fuel-stopped in Paris because we had to have enough fuel to get out of where we were going. There was no fuel there. There turned out to be, in fact, nothing there but a very narrow, short (for a 747) runway surrounded by farmland, no buldings save for a couple of construction trailers. I wasn't given the information for the destination until just before departure in Paris. Enroute from Paris, looking at the approach plate and runway data, I saw two problems. The destination weather was forecast to be overcast, but with the ceiling high enough that we would be able to get in using the only approach aid available, an NDB. However, the airplane we had been dispatched with had an ADF that had only a pointer bug rather than a full needle. Our ops specs prohibited NDB approaches without a pointer needle with a tail. I ignored that problem. The second problem was that the taxi chart showed a runway too narrow to turn around on without getting a wing gear off the edge. There were no taxiways, no turnarounds, no ramps. This caused a series of contacts on HF via Stockholm Radio (no Satcom on this old airplane) between myself, dispatch, and our director of operations. The final call from the DO was to tell me he had talked to the military and that though the airport plate didn't show it, there was now a small ramp at each end of the runway. We landed, unloaded, and departed without incident.
Frustration Over Things I Couldn't Control
This category was large, most minor, some laughable even, some of more consequence, but all for me irritating. Things like being lied to by ground support people, crappy accommodations (I and a flight engineer got body lice from a stay at the Hotel Carrera in Santiago, Chile), having to pay bribes (especially in Indonesia and Egypt), having to sometimes wait hours for immigration clearance, often having to first say "salaam alaikum" on initial contact with Saudi Arabian controllers before they would answer , having to switch back and forth between saying Bombay or Mumbai during the name switch. Hindu nationalist controllers wouldn't answer unless you said Mumbai, others wouldn't answer unless you said Bombay.
The incident I most remember in this category is when I, a first officer, a flight engineer, and 14 flight attendants commercialled to Medina, Saudi Arabia to pick up a flight. After we got there, we were told the airplane was going to be at least 12 hours late. No problem, hotel time, as the rule was we were entitled to a room if there was to be more than a five hour delay. However, problem, there were no available accommodations in the airport area. There were rooms available in the city but, like Mecca, non-muslims cannot enter Medina. We sat for 14 hours in a terminal with pathetic air conditioning in the middle of summer before the airplane arrived.
One final small irritant. We kept having to give up our usual parking area at Tel Aviv to SAM 28000 and SAM 29000 during the latter months of Bill Clinton's time in office as he was making last ditch efforts to broker an Israeli-Palestinian peace.
So, stressful, definitely, but it was the highlight of my life, and I'm glad I did it all, including all that wasn't so great at the time.

I could imagine the stress on the body is a good deal.  Heck, I just sit at my desk writing computer code and the result is physical therapy, back injections and chiropractor visits.

Not many jobs where you can kill hundreds of people or lose your entire career by making a simple mistake. And your every move is being recorded. Add to it that you're doing nearly the same thing over and over, but can't miss any tiny detail.

Any job where you drive a car/truck, really any kind of motorized vehicle, has the potential to kill people & end your career & own life. Pilots & passengers really should be more worried driving to & from the airport, not worrying about the actual flight. And if you're worried about someone watching you work, maybe you're not qualified to have that job.

What Xen2050 said. A truck crashing full-speed into the end of a traffic jam during holiday season will easily kill a dozen people and more. And in car traffic, your chances of surviving a crash that killed other people are much higher than in the cockpit...

Don't forget the trains, where you can injure people by simply applying emergency brakes because you just saw people/cars on the tracks.

And surgeons/nurses can lose their entire career by making a simple mistake that can be fatal to their patients.

Surgeon / nurse can't kill hundreds, and every word and action isn't recorded to review their every decision when something goes wrong.

I am not a pilot, but just on top of my head:

Stressful situations which require high amounts of attention to the smallest details
Responsibility for human lives
Tight schedules with small amount of time to rest

The flight duration doesn't matter, extreme situations can occur at all times.

Why is being a commercial pilot stressful? On a normal flight, the pilots take off, communicate with ATC, change some parameters in the navigation computer from time to time, and land.
While on the ground, the pilots have to visually inspect the aircraft and prepare the whole flight. This includes flight-planning, analysis of weather-forecasts, fuel calculations and many more things.
Specially on short-haul-flights, every minute counts. If a plane arrives ten minutes to late, passengers could miss their next flight. Every following flight of this late airplane gets delayed too. This is a stress-factor for pilots.
From Phantomazi's answer:

Stressful situations which require high amounts of attention to the smallest details
Responsibility for human lives
Tight schedules with small amount of time to rest

As you can see, the flying might not be the part which is most stressing for the pilots. What's stressing is the whole thing around.

But can a pilot really do something about being late? Does he care? When my bus is late because of traffic and bad weather I don’t blame the bus driver and I don’t expect him to be stressed or very sorry about it.

@Michael My thoughts exactly. When some regulation, some jerk in the tower, some severe weather or any other external factor prevents me from getting my task done, I'll tell the people affected and wait until we can move on. No need to be stressed. - Hopping from one end of the world to another, different continent every day, (too) tight timeslots for flight preparations &c. would stress me way more.

@Michael Imagine you are sitting on a plane in sweden. You are already 15' late, you know you have to be back in switzerland at a certain time because there is a long haul flight waiting with 300 and more passengers. You don't know exactly how much you have to wait more. Every minute could cost your company money. From landing in switzerland to taking off again, you will be very stressed to minimize the time you are late. Of course not every airline pilot thinks that way, there will be people who just don't care that much about time. Anyways, I know a lot of people that are stressed by this.

@jklingler Does 15' mean 15 minutes?

@FuriousFolder Yes Sir

@Michael  IT is generally recognised that the difference between 'pressure' and 'stress' is what you have control over - normal landings are high-pressure, but aren't stressful as such, because they are largely down to the skill of the pilot. Making up lost time is largely out of the pilots control, so IS stressful.

There are a lot of things that can make the job of a airline pilot stressful.

The non flying duties of the job are the most stressful: Such as getting the airplane ready to push off the gate. Meaning all of the tests and checks and planning that must be done in possibly a 30 minute window.
Scheduling: Every time they call you take a deep breath before answering the phone because you know that most likely, whatever they are planning to tell you, is going to screw up your plans for the day and possibly the week. Most pilots have a special ringtone set for their phone number to pre-warn them when its crew scheduling on the phone.
Passengers: Its not that we don't like passengers we just get tired of them complaining about everything and slowing the embarkation and debarkation process. I fly regional jets and we always hear about how small the airplane is. Someone will inevitably argue with the flight attendant for five minutes that their bag, that is the size of a small child, will fit in our tiny overheads because it fit on their last flight. When asked about the aircraft they were on last we find out that it was a 787 on a international flight. I had a passenger 2 days ago ask me if I was a F18 pilot because he thought I braked to hard on the landing. Passengers will find whatever they can to complain about, its like a sick game for them. Now i'm not saying that all of them are bad, some passengers are very nice and grateful and will thank you for getting them there safely.
Fuel: When we get our paperwork for a flight it tells us how much fuel is going to be put on the aircraft and how much we must have before we can take off. A lot of times this is just enough fuel to complete the flight with the FAA required reserve amounts. They do not like to give extra fuel because that means more money in fuel, the possibility of being weight restricted and having to leave passengers and bags behind, and its costs money to carry fuel because the heavier you are the more fuel you will use. Often times if we know we are going to be waiting for a while on the ground for takeoff or we decide that there is a possibility of us having to hold for a while in the air waiting to get cleared into a busy airport we have to call our dispatcher and ask for contingency fuel. This can be like pulling teeth sometimes. Its unbelievable that we have to argue with them to get more fuel on the aircraft because we think it will result in the safest outcome.
Being on time: Part 121 air carriers are big about being on time especially when you work for a fee for departure airline (most regionals are). We have a OUT time where we should be off the gate and they expect us to be off the gate no more than ten minutes early but not a minute late. Then we have a time that we are expected to arrive. They would like us to arrive either at the listed time or within 14 minutes after but not before the listed time and not 15 minutes late if we can help it. Then we have a computer system that tells us how fast we should fly to save fuel and money and make this all happen, it often gets ignored.
ATC Delays: ATC plays a large role in some of our stress. Things like ground stops and diversions make like fun. If a place like Newark NJ gets too busy they will ground stop meaning that anyone who is getting ready to go there who hasn't taken off yet is going to be sitting for a while until they clear up the traffic jam in the sky. We say for an hour and a half one night to takeoff to go there. This meant that the rest of our evening was delayed an hour and a half as well, evening getting to go to bed was delayed for us that night.
Commuting: As much as the public must think its awesome that we get to travel all the time it gets old really fast. We are often not based close to our homes which means we have to commute to work. Sometimes it is easy to get a seat and we have no problem. Other times all the flights are full and we have to try to squeeze in somewhere or hope that we can get the cockpit jumpseat. We don't mind sitting next to passengers on flights. However, we do mind when you try to make us your private source on everything aviation related. We don't mind answering a question or two but I don't want to sit there and explain the mechanics of a jet engine to you and explain to you why it is so turbulent. Also just because we are a pilot does not mean we know everything about every aircraft. Just because we are flying to Houston TX on a 737 does not mean that I fly that aircraft and know anything about it.
Medical Examiners: As airline pilots we are required to see a medical examiner once per year to ensure that we are fit to fly. We are always worried about our health and whether or not they are going to find something small that would prevent us from flying. They are constantly changing the rules on us and its hard to keep track of them all, all of the time.

Next time you are on a commercial flight just remember that the crew is there to get you from point A to point B safely and efficiently. We all really do love what we do or we wouldn't be there because lets be honest...the pay isn't that great. Thank them for a nice ride and smile....they will appreciate it.

I remember a very wet landing, the rain was coming down in sheets. On my way off the plane, I saw the pilot, and said - nice ditching! He got a good chuckle out of that.


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Can a someone with just a PPL log PIC time on a non-transport commercial flight?
I have a job that requires me to travel on a small company plane with a company "commercial"pilot. I only have my PPL. If I am certified in the type of aircraft may the pilot allow me to fly "solely manipulate the controls" of the aircraft, while he clearly remains the PIC and responsible for the flight? If I am rated in the aircraft could I log those hours?

This is not a Transportation Operation, and operates under CFR 14 Part 91 regulations.

there is another issue, which is whether or not the insurance company will permit you to manipulate the controls. Many policies have only "named pilots," and there is a special rider that needs to be added to allow other pilots to fly it, with certain aeronautical experience, training, and time in type.

Yes, you can log PIC in an aircraft category and class that you are certified to fly. You can log that time during which you are the sole manipulator of the controls. This is the case even if another crew member (the commercial pilot) is the acting PIC.
See 14 CFR 61.51 (e) for this and other situations allowing logging of PIC.
Following is the relevant section of 61.51 (e):

(e) Logging pilot-in-command flight time. (1) A sport, recreational,
  private, commercial, or airline transport pilot may log pilot in
  command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an
  aircraft for which the pilot is rated, or has sport pilot privileges
  for that category and class of aircraft, if the aircraft class rating
  is appropriate;

Thank you so much for your response! Would the Commercial Pilot also log PIC time due to the fact he's still solely responsible for the flight or would I only be able to log PIC for the hours I'm flying?

Thank you again so much! The aviation community is the best. Happy Holidays!!!

While I totally agree with the posted answer (yes, the PPL can log PIC while sole manipulator), Im not sure I agree that the actual PIC can't log the entire flight.  He IS the PIC.  There is FAR 61, but there is also FAR 1 -- which is essetially "signed for the aircraft" as the definition of PIC.  Thus an airline captain logs every leg as PIC, even those legs the first officer was the sole manipulator. The FO can log his legs as PIC per Part 61, but the captain is the PIC per Part 1.

Remember that logging PIC and acting as PIC are different. Just because someone is PIC doesn't mean they can log it. Airline pilots can log PIC because the aircraft they fly are certified for multiple pilots. If they were flying a 172 in a Part 121 operation, only one could log PIC.

@RalphJ Acting as PIC and logging PIC are distinct concepts.

@RalphJ this is settled law. acting PIC cannot log if someone else is logging as SMOTC.

"However, two pilots may not
simultaneously log PIC when one pilot is
sole manipulator of the controls and the
other is acting as pilot-in-command if the regulations governing the flight do not require more than one pilot." https://www.faa.gov/about/office_org/field_offices/fsdo/sdl/local_more/avsafety_program/media/LOGGING%20PILOT-IN-COMMAND%20TIME.pdf

@RalphJ The last comment by rbp is key: "if the regulations governing the flight do not require more than one pilot".  The only situations where more than one person may log PIC time are the situations which require more than one pilot.

@DavidSchwartz There is no rule allowing any required crew member to log time, only required pilot flight crewmembers. Additionaly, though it doesn't appear to apply to the situation described in this question, in some aircraft or operations an ATP can log PIC time just because they are acting PIC.

Please note that being PIC and logging PIC are different things.
FAR 1.1 defines the Pilot in Command as the person who,

(1) Has final authority and responsibility for the operation and safety of the flight;
(2) Has been designated as pilot in command before or during the flight; and
(3) Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

Basically, at any given time, there can only be one acting PIC on a flight, no matter how many pilots are on board the aircraft.
According to 14 CFR 61.51 (e):

(e) Logging pilot-in-command flight time. (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;
(ii) When the pilot is the sole occupant in the aircraft;
(iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted; or
(iv) When the pilot performs the duties of pilot in command while under the supervision of a qualified pilot in command provided,
...

The end result is that more than one pilot can log PIC time when there can only be one PIC on a given flight.

Yes, there are times when more than one pilot can log PIC, but not in the situation described by the OP...


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How could a twin aisle aircraft (Boeing NMA) ever have a single aisle (A321) economics?
I understand from this discussion about the Boeing 757 and 767 that drag is directly related to the front area of the airframe, hence flight efficiency of the dual aisle aircraft can only be significantly inferior to the single aisle design.
So how should we consider current Boeing reflection in the design of the so called MOM or NMA that they seek a twin aisle aircraft with single aisle economics? They are reported to aiming at offering "twin-aisle capabilities—range, comfort, capacity, and faster turnaround time—with single-aisle economics". Is it pure marketing rhetoric or are there parameters other than front area in the equation of such an airplane that would make the assertion sound?

Improved streamlining? It reduces penalty from front area being larger and the increased mass/surface area would hurt a smaller plane more due to the scaling. Agree with ymb1 about it probably being marketing talk with some aspirational "we must improve our economics" thrown in.

So it's definitely not ALL marketing spin, but it's also definitely not ALL engineering, either.
The frontal area is absolutely a major component of the drag on an airplane, but wingtip devices (sharklets, winglets, etc.) can significantly reduce drag, as can better nose shapes, smoother surfaces, and a number of other design considerations.  If you kept all these other things the same, then increasing the frontal area would increase drag and reduce efficiency, but these other things aren't the same in a new airplane.  The MoM proposal would certainly take advantage of all sorts of wing, engine, airframe design improvements that would reduce the drag components, and then you'd gobble most if not all of that up by making the airplane wider.  ;-)
If I'm putting on my "engineer but worked in marketing for a while" hat, I'd say that the challenge put to me is that the marketing people want an airplane that can be operated at what used to be called single-aisle efficiency, but can now be done with widebody seat capacities.
I'd also contend that of the parameters mentioned: "range, comfort, capacity, and faster turnaround time" the only one of those things that really requires you to think seriously about a twin-aisle airplane is capacity.  I can build a single-aisle aircraft that has every bit as much range, way more comfort, and a much faster turn around time as a twin-aisle aircraft, it just doesn't hold as many people.  ;-)

Using “wingtip devices” and “significantly” in the same sentence is wrong. Wingtip devices are aerodynamically never better than extending the wing, which is why they are still rare on new designs (main use is if they can make the plane fit in a smaller stand). They have some advantages over extending the wing for redesigns. In line with that, it is the A321-NEO that got fancy winglets while the early 797 concept pictures have none.

We can argue what qualifies as "significant" then... the question was in the context of economics, so if something provides a "significant" benefit relative to the cost, it gets implemented.  Given how many of these wingtip devics are installed or were retrofitted, the airlines certainly seem to think that the investment is worth it.

Drag is first and foremost proportional to weight. If you can make the plane lighter, it will need less energy to fly. And the new carbon fibre composite structures promise just that. So a new design is likely to be lighter than the all-aluminium A321, which should more than make up for the increase in drag due to bigger cross-section.
Efficiency means cost per seat-(or tonne-)mile and there are many more factors to that than just fuel cost and most of them are fixed costs, paid by day whether the plane is moving or not. If the plane can turn around faster due to its two aisles, it can fly further in a day and thus it will more efficient as the fixed costs will be spread over more miles. It would also help if they could make maintenance easier.

A reference/link to support/quantify the statement about drag being proportional to weight would greatly help this answer.  I would contend that it it not at all obvious to most readers whether a 5% increase in frontal area results in {more, less, or about the same} additional drag compared to a 5% increase in weight....


text:
Is it ever possible to auto-rotate with a missing rotor blade?
A couple of years ago a UH-60 managed an auto-rotation landing with "badly damaged rotor blades."  (Couldn't find further details on that incident.)
Is it ever possible to auto-rotate in a helicopter that has lost a segment or entire blade of a main rotor?
My guess is that, in general, it would be impossible to control the lift asymmetries and such in-flight damage would always result in an uncontrollable crash.  If that's correct, then what about the special case of a helicopter with 4 or 6 main rotor blades, and if it were possible to jettison the blade opposing the one that was lost or damaged?  (Are any helicopters equipped with an emergency ability to jettison rotors in flight, other than the ones with vertical ejection seats?)  Is it known whether such a damaged rotorcraft can reliably auto-rotation in that scenario?

I found another view of the damage. I reckon any rotary pilot would look at that and ask how they walked away.  I certainly do. Remarkable.

That incident was a complete freak. It looks like a delamintation of the trailing edge of the blade with subsequent loss of large portions. The UH60 has a fully articulated head which allows for the blades to move freely and independently up and down and forwards and backwards as they rotate. With power removed (the pilot entered autorotation), the enormous out of balance forces generated were absorbed by the hinges (we know this because the thing didn't disintegrate). In summary, they are alive because they had 4 blades on an strong articulated head and a huge dose of good fortune.

Highly improbable. If you've ever seen how much a washing machine can shake with a little imbalance in the laundry, at a relatively low energy spin, imagine the destructive forces that would be experienced by the imbalances in your theoretical rotors. Even if your missing blade manages to get away without causing impact damage to the other blades, there is going to be an immediate violent force translated through the aircraft. Your newly configured rotor formation is still going to try to spin around its center of mass, which is no longer concentric with the mast. The degree of imbalance will tell you how far off center the new center of rotation wants to be. The mast is still going to be trying to keep the rotor rotating on its own center, so now the rotor and mast are fighting to circle their common center, and basically this means the rotor, it it doesnt just go to pieces from all this force, will be yanking HARD and fast on the mast, which would probably rip it off the airframe.... but, if your magic rotor and mast stay intact, the violent motion would be translated to the airframe which will now be shaking super violently around you, which would likely cause it to rapidly disassemble. If it magically stayed together, the people inside (hello pilot) would be experiencing forces through the body like riding the paint shaker at the hardware store, but harder and farther, if not faster, on every shake. Watch that paint shaker and imagine your head being in that.
I do not believe your scenario would be survivable, even on the ground. It's odd to think, but a complete rotor disintegration is not the worst thing that could happen after blade loss.

Ah, the rapid unplanned disassembly. Happens every once in a while in spaceflight, too. https://space.stackexchange.com/q/10022/415

"Every once in a while" in space flight? Clearly you've never watched me play Kerbal Space Program

@JonStory: Quick, revert to VAB!

It would be impossible. A rotor blade that has lost a large segment, or entire blade of a main rotor, would be so badly out of balance that it would immediately self destruct.


text:
What are these things under Airliners wing?
As the picture below, what are these triangle components for? I find these normally installed under the Flaps. Thanks!!

Those are called anti-shock bodies and are placed on the wing to reduce wave shock drag.

Of course one could argue it's a chicken-egg-problem. But I think the designers put the actuation system for the flaps under the wings because those are really needed. And they will cover them aerodynamically. Only then they will look at the area-rule and might adjust the size of the cover. They will certainly not start with "anti-shock bodies" and figure out later on if the actuation system will fit inside.


text:
How are the structural failures reported to pilot
For instance an engine separated from aircraft (though most unlikely 1E-13 probability)  or wing got damaged, how is it reported to the pilot?
Will it be reported as 'Engine Fail' or 'Left Wing Fail'?
If so, how is pilot supposed to know if it is a functional failure or a structural failure?

The cockpit windows provide really good information about the state of the airframe.

@abelenky - on a C172, perhaps... not so much in a 747 or A380. See Quantas Flight 32, for example, or El Al Flight 1862 - in neither case could the pilots properly inspect the damage from the cockpit. For QF32 the third pilot went to inspect through the passenger windows, for LF1862, they couldn't inspect it at all (cargo 747) and crashed, partially as a result of not being able to understand the damage properly

@fooot while similar, I don't agree that this question is a duplicate of the one you posted: they both address very different kinds of failure, and the answers on that question (or the one it itself is marked as a duplicate of), do not answer this question. Voting to leave open

I would think the pitch of your co-pilot's voice would indicate a problem of this severity. More seriously, would anyone bother to set the reserved code on the transponder for example?

@JonStory seems to me like they're both asking about what happens when an engine falls off, not sure how the two are very different kinds of failure.

This mentions losing an engine as one example of structural failure, but is about more generic structural failure. There's no answer elsewhere about 'how does the pilot know if the last 3 feet of the wing snaps off?' For example. Take the focus off the word engine and it's quite a different query to my eyes

@JonStory you may have a point there... maybe it should be edited to make it more distinctly different. The answer is pretty much the same regardless... most things will have no specific warning, but would have to be deduced from the failures of related systems.

Incidentally, astonishingly engine separation procedures do exist (a very general document for turboprops): http://www.cast-safety.org/pdf/1_basics.pdf

The linked duplicate question is itself closed as a duplicate of yet another question

authors: ณรงค์กร ชูวงษ์วาน


text:
Is optimal landing flare related to ground effect?
Based on other questions it appears that a "flare" is always part of a healthy airplane landing.
This question asked when a flare should be started, and I found it interesting that the accepted answer expressed it in terms of altitude.  Which got me wondering: Is the need for a flare a consequence of ground effect?  And the optimal flare height for a particular airplane a function of when it enters ground effect?

Regarding the first sentence: no, not always. Those questions were in the context of airliners and GA. As mentioned in some answers already, there are normal landing techniques where flare is not performed: e.g. landings on a carrier.

It depends on the type of landing.  If you are doing a normal landing on a normal runway, the round-out and flare are required steps to put you in a position to be in level-ish flight just above the runway (the roundout), and controlling the touchdown by trading inertial energy for increased lift by pitching as you feel for the surface (the flare).
Ground effect has an effect on the flare phase by giving you more energy margin if the ground effect is strong.  So a low wing airplane with large flaps with a strong ground effect will have a lot more support from ground effect than a high wing airplane with small flaps that has weaker support from ground effect.  If ground effect wasn't there, it wouldn't really change how you land too much, except you may tend to carry power into the landing more, or arrive with a bit more energy by increasing the approach speed a bit.  In some airplanes the ground effect is much more pronounced than others (they like to float).
There are landings where you don't really flare at all.  In an extreme STOL approach, you fly to the surface already in the landing attitude, controlling descent rate with power and maybe little pitch adjustments only as required for speed corrections.  If the engine quits during such an approach close to the ground you are out of energy, already "flared" and will land hard and you live with that risk if you're doing that sort of thing.
And of course, there is no flare in aircraft carrier landings.  You fly a constant descent into the ocean, and the carrier's deck just gets in the way of your descent.

Yes, optimal flare is related to the ground effect (i.e. must take it into account), but is not a 'consequence' of it.
In a way, it's the opposite. Flare does two things: primarily, it arrests your sink rate for a gentle touchdown, and also sets a correct attitude. If the airplane has a particularly strong ground effect, this effect will reduce your sink rate and 'cushion' your landing, without you doing much. There may be secondary effects though, which will require you to actively control attitude (pitch).
A case in point is Concorde. Due to its wide-chord wing and high angle of attack on approach, it had a very strong ground effect. So much so that it didn't require flare at all. However, this ground effect produced a strong pitch-down moment, which required the pilot to pull the yoke in order to maintain the attitude. As a result, the landing felt somewhat 'normal' for the pilot, except that the aircraft didn't pitch up and landed in the approach attitude.

The flare, or roundout, is performed as a part of landing in order to accomplish two things: 1) Arrest the rate of descent on the approach and 2) place the aircraft in the proper attitude for it to gently touch down on its landing gear.  For tricycle gear airplanes, this is typically a nose high attitude so it will make contact with the runway on its main landing gear only.  Critical to a good flare is arriving at the entry at the proper approach airspeed to minimize the float prior to settling onto the runway, typically Vref = 1.3*Vso + gust factor.  This provides just enough energy accomplish your two flare tasks prior to the airplane being exhausted of energy and settling down onto the runway.  Ground effect will amplify the time and distance covered during the round-out if the approach speeds are not correct, since it is reducing induced drag on the airframe, requiring longer times to exhaust the airplane of energy prior to touchdown.
The optimum height to begin the roundout depends upon the airplane in question, it’s approach speed, handling characteristics, etc.  Typically small GA aircraft will begin this process at about 10-12 ft above the runway.  Large transport category aircraft will begin this about 20-30 ft AGL.  Just prior to touchdown the airplane will be approx 1-2 ft above the ground and in the proper landing attitude, if the flare was accomplished properly.


text:
How does afterburner efficiency vary with thrust?
Afterburners are much less efficient than turbine engines at converting fuel into thrust, so AFAIK no jet will engage afterburner unless it is already at full throttle on the turbine.
But what if an afterburner were used at less than full throttle?  How, if at all, is the efficiency of an afterburner related to the thrust of the engine feeding it?

When simulating the engines in afterburner mode, the efficiency is calculated based on various effects in the afterburner. The efficiency is based on FAR (fuel air ratio), pressure and flow Mach number.

Normally, what is throttled back is the afterburner. The principle of reheating an already hot gas is so inefficient that partial wet thrust is achieved by running the engine at full power and using less than full afterburner.
The efficiency of the afterburner is proportional to the ratio of gas temperatures (peak to entry temperature), but at partial jet thrust the pressure level and volume flow in the jet exhaust is also diminished, so the available thrust increase from the afterburner will also decline sharply. To produce the same thrust, it will be much more efficient to run the jet at full speed and to throttle the afterburner.
The Tornado attack aircraft, designed for nap-of-the-earth flight, was so inefficient at higher altitudes that during the Bosnian war of the mid-Nineties it had to run one engine in partial afterburner in order to keep up with the tanker aircraft. For inexperienced crews which used most of their allotted time for coupling with the tanker, the tank stop could result in a negative fuel gain because so much was needed to keep up with the tanker.